Constant velocity universal joint

ABSTRACT

A constant velocity universal joint for transmitting torque, having an outer joint part with outer ball tracks, an inner joint part with inner ball tracks, torque transmitting balls guided by pairs of outer and inner ball tracks positioned in corresponding meridian planes, and a ball cage which receives the balls in circumferentially distributed windows and holds same in a common plane and guides same on to the angle-bisecting plane when the joint is ariculated, with the center lines of the outer and inner ball tracks being composed of at least two differently curved portions adjoining one another, with the center lines of the ball tracks of the outer joint part each comprising convexly curved inner portions and, towards the open end, concavely curved end portions.

BACKGROUND OF THE INVENTION

Description

The invention relates to a constant velocity universal joint fortransmitting torque, having an outer joint part with outer ball tracks,an inner joint part with inner ball tracks, torque transmitting ballsguided by pairs of outer and inner ball tracks positioned incorresponding meridian planes, and a ball cage which lodges the balls incircumferentially distributed windows and holds the balls in a commonplane and guides the balls on to the angle-bisect-ing plane when thejoint is articulated, with the center lines of the outer and inner balltracks being composed of at least two differently curved portionsadjoining one another.

Joints of this type are known as Rzeppa fixed joints (RF) orundercut-free fixed joints (UF). The latter are described in DE-PS 22 52827. For a certain size of such joints, and especially as regards theaxial length of such joints, there exists a mutual interdependencebetween the maximum articulation angle and the thickness of the shaft tobe connected to the inner joint part. On the one hand, the articulationangle is limited in that the balls must be prevented from leaving thetrack ends, or, to be more precise, as far as edge loads at the trackends are concerned, it has to be ensured that there exists a sufficientsafety distance between the point of contact of the ball in the trackand the track end edge. Furthermore, the articulation angle is limitedby the thickness of the connecting shaft which, upon articulation of theinner joint part, abuts against an inner cone of the outer joint partand thus prevents further articulation. It makes sense to adapt thethickness of the connecting shaft and the shape and position of theinner cone to one another in such a way that said abutment of theconnecting shaft coincides with the safety distance between the point ofcontact of the ball and the track end edge.

Developments in automotive engineering are such that said constantvelocity universal joints are expected to have an ever increasingperformance, which means that with a predetermined available space andmass, the service life and functional scope have to be increased, or,vice versa, with a predetermined service and functional scope, space andmass have to be reduced.

With prior art joint designs, any improvements on the one side, forexample in respect of the articulation angle, can only be achieved byshortening the service life and reducing the breaking strength.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide a joint of theinitially mentioned type whose performance is improved in such a waythat space and mass can be reduced without adversely affecting theremaining parameters.

In accordance with the invention, the objective is achieved in that thecenter lines S of the ball tracks of the outer joint part each compriseconvexly curved inner portions S₁ and, towards the open end, oppositelycurved concave first end portions S₂ and that the center lines of theball tracks of the inner joint part each comprise curved outer portionsand, towards the base end of the outer joint part, oppositely curved,second end portions wherein the inner portions S₁ and the outer portionseach extend in a curved way around a center Z₁ inside the outer jointpart, and the first end portions S₂ and the second end portions eachextend in a curved way around a center Z₂ outside the outer joint part.This means that the inner portions S₁ extend at least partially in acurved way around a joint center C and that the first end portions S₂positioned towards the open end are curved in the opposite direction,i.e. outwardly. In general, the result is that the distance of thecenter lines of the ball tracks in the outer joint part from the axisA_(A) in the first end portions S₂ increases towards the open end of theouter joint part.

The shape of the outer joint part is hence characterised in that theends of the ball tracks widen and radially move away from one anothertowards the open end of the outer joint part.

Preferred embodiments of the invention are described in furthersub-claims to which special reference is hereby made.

Due to general conditions of symmetry, the ball tracks in the innerjoint part widen and move away from one another in an end portion at theaxially opposite end, i.e. towards the base of the outer joint part,again with reference to the center lines of the ball tracks whosedistance from the axis A_(I) of the inner joint part is thus greatest atsaid end.

In accordance with certain lines of curvature, said first end portionsS₂ can extend as circular arcs for example, but the end portions of thetracks can also extend in straight lines at an angle relative to thelongitudinal axis A_(A).

The effect achieved by the track shape in accordance with the inventionconsists in that—in contrast to joints in accordance with the state ofthe art wherein the points of contact of the balls in the tracks arepositioned approximately in radial planes extending through therespective centers of the balls—there is achieved an axial distancebetween the points of contact of the balls in the tracks with referenceto the radial planes through the joint centers, with the points ofcontact being offset towards the central joint plane. In this way, it ispossible to achieve improvements regarding the relationships of theparameters of joint length/joint mass, maximum articulation angle andthickness of the connecting shaft. As far as further explanations of theinventive measures and effects are concerend, reference has to be madeto the following drawings. In the embodiment illustrated, the inventivejoint is shown as a UF joint. However, to put the technical teaching inaccordance with the invention into effect, it is not necessary for theball tracks to be undercut-free.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a longitudinal section of an undercut-free constantvelocity universal joint (UF joint) according to the state of the art.

FIG. 2 shows a track run-out of the outer joint part of the jointaccording to FIG. 1.

FIG. 3 shows the outer joint part of the joint according to FIG. 1 withan articulated connecting shaft.

FIG. 4 shows a longitudinal section of an inventive constant velocityuniversal joint with undercut-free tracks (UF joint).

FIG. 5 shows a track run-out of the outer joint part of the jointaccording to FIG. 4.

FIG. 6 shows the outer joint part of the joint according to FIG. 4 withan articulated connecting shaft.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a prior art constant velocity universal joint whichcomprises an outer joint part 11, and inner joint part 12, torquetransmitting balls 13 and a ball cage 14. AT one end, the outer jointpart 11 is closed by a base 15 which is followed by a joint journal 16.An aperture 17 of the outer joint part 11 is provided axially oppositethe base 15. In the outer joint part 11, there is shown one of aplurality of circumferentially distributed outer ball tracks 18 which,if viewed from the open end 17, is undercut-free and has a center lineS_(a). The inner joint part 12 is provided with a central aperture 19into which there is inserted a connecting shaft 20 which is axiallysecured by a securing ring 32. In the inner joint part 12, there isshown one of a plurality of circumferentially distributed inner balltracks 22 which is also undercut-free if viewed from the open end 17 andhas a center line S_(i). Outer ball tracks 18 and inner ball tracks 22are associated with one another in pairs and jointly accommodate inpairs the torque transmitting balls 13. The balls 13 are jointly held inone plane by the ball cage 14 in that the balls are inserted into thecage windows 23 in the central cage plane which coincides with thecentral joint plane E. The ball track center lines S_(i), S_(a) areparallel to the respective ball track ground lines. Both center linesS_(i), S_(a) are symmetrical to one another with respect to plane E.

The central joint plane E also contains the joint center C which isdefined by the point of intersection of the axes A_(A), A_(I) of theouter joint part and inner joint part when the joint is articulated. Atthe open end 17 of the outer joint part l, there is provided an innercone 24 which forms a stop for the connecting shaft 20 of the innerjoint part 12 when the joint is articulated and thus limits thearticulation angle β of the joint, as described below.

FIG. 2 shows the outer joint part 11 with an outer ball track 18 in abroken-away manner. Said inner cone 24 which cuts off the outer balltrack 18 at the open end 17 is still visible. Furthermore, there isshown a ball 13 in the ball track 18 in a position which is assumed bythe ball 13 when the inner joint part is articulated by its maximumamount relative to the outer joint part. In this case, the maximumarticulation angle β between the axes, which will again be referred tobelow, leads to an articulation angle of the cage relative to the outerjoint part of β/2 which is shown in the drawing. By correspondinglyarticulating the central plane of the cage relative to the central jointplane E, the ball 13, too, is moved out of the central joint plane E bythe angle β/2. The center M of the balls follows the dash-dotted centralline of the outer ball track 18 which is defined by a circular arc S_(a)with the radius R₁ whose center Z on the axis A_(A) is offset by theoffset O₁ relative to the central joint plane E, and by a straight lienG following same tangentially and extending parallel to the axis A_(A).In the ball position as illustrated, the contact point B of the ball inthe outer ball track 18 is positioned in a radial plane through the ballcenter M. Relative to the track end edge defined by the inner cone 24,the contact point B is at a minimum axial distance L which, in view ofpossible edge breakages at the track end, must not be allowed to bereduced. The distance between the contact point B and the central jointplane E has been given the reference number N.

FIG. 3 shows the above-mentioned joint articulation angle β between theaxis A_(A) of the outer joint part 11 and the axis A_(I) of the innerjoint part 11 in the joint center C. In this case, the connecting shaft20 replaces the inner joint part; in this position, it comes to restagainst the inner cone 24. By thus limiting the degree of articulationto the angle β, the minimum distance L between the contact point B andthe track end edge of the ball track 18 is ensured.

FIG. 4 shows an inventive constant velocity universal joint whichcomprises an outer joint part 31, an inner joint part 32, torquetransmitting balls 33 and a ball cage 34. At one end, the outer jointpart 31 is closed by a base 35 which is followed by a joint journal 36.An aperture 37 of the outer joint part 31 is provided axially oppositethe base 35. In the outer joint part 31, there is shown one of aplurality of circumferentially distributed outer ball tracks 38 which,if viewed from the open end 37, are undercut-free, without this beingabsolutely essential. The inner joint part 32 is provided with a centralaperture 39 into which there is inserted a connecting shaft 40 which isaxially secured by a securing ring 41. In the inner joint part 32, thereis shown one of a plurality of circumferentially distributed inner balltracks 42 which, with reference to the central joint plane E, extendssymmetrically relative to the outer ball track and—if viewed from theopen end 37—is undercut-free. Outer ball tracks 38 having center linesS_(a) and inner ball tracks 42 having center lines S_(i) are associatedwith one another in pairs and jointly accommodate the torquetransmitting balls 33, wherein each ball is held in the point ofintersection of the associated center lines S_(a), S_(i). The balls 33are inserted into cage windows 43 in the central plane of a ball cage34, which coincides with the central plane E of the joint, and arejointly held in one plane by the ball cage 34. The central joint plane Ealso contains the joint center C which is defined by the point ofintersection of the axes A_(A), A_(I) of the outer joint part and innerjoint part when the joint is articulated. In the outer joint part, onthe side of the open end 37, there is provided an inner cone 44 whichcan form a stop for the connecting shaft 40 when the joint isarticulated. The center lines S_(a), S_(i) of the ball tracks 38, 42which extend parallel to the respective track base and which intersectone another in the center of the ball 33 comprise turning points T₁, T₂.It is an important aspect that the outer ball tracks 38, towards theopen end 37, move away from the longitudinal axis A_(A), for example inthat a center of curvature of the end portion of the center line S_(a)of the outer ball track 38 is positioned outside the outer joint part 31and said center line S_(a) respectively. Accordingly, the inner balltracks 42, towards the base end 35, move away from the longitudinal axisA_(I) in that the center of curvature of the end portion of the centerline S_(i) of the inner ball track 42 is positioned outside the innerjoint part 32 and said center line S_(i) respectively. The center linesS_(a), S_(i) are each composed of at least two differently curvedportions adjoining one another, to be described more detailed withreference to FIGS. 5 and 6.

FIG. 5 shows the outer joint part 31 with the outer ball tracks 38 in abroken away manner. It is possible to see said inner cone 44 which cutsoff the outer track base 38 at the open end 38. Furthermore, the ball 33of the ball track 38 is shown in the position which it assumes when theinner joint part is articulated relative to the outer joint part by theunchanged joint articulation angle β. The joint articulation angle βbetween the axes, which will be referred to below, leads to anarticulation angle of the cage relative to the outer joint part of β/2which is shown in the drawing. With the central plane of the cage beingarticulated accordingly relative to the central joint plane E, the ball33, too, is moved out of the central joint plane E by the angle β/2 intothe angle bisecting plane W. The center M of the ball follows thedash-dotted central line S_(a) of the outer ball track 38 which isdefined by a first circular arc S₁ with the radius R₁ whose center Z₁ onthe axis A_(A) is offset by the offset O_(z1) relative tot eh centraljoint plane E, and by an adjoining second circular arc S₂ with theradius R₂ which is less than the radius R₁ and whose center Z₂ on astraight line extending outside the joint at a distance O_(Y2) from thelongitudinal axis A_(A) is offset by the offset O_(Z2) relative to thecentral joint plane E. The first end portion S₂ of the center line S_(a)continuously adjoins the inner portion S₁ of the center line S_(a) in aturning point T_(1.2) respectively. Tangents on the center line S_(a)are axis-parallel in the respective turning points T_(1.2). The innerportion S₁ of the ball tracks 38 in the outer joint part 31 extend by10° beyond the central joint plane E towards the open end 37 of theouter joint part 31.

With the articulation angle β assumed to be unchanged, the ball center Mis slightly displaced towards the central joint plane E. On the otherhand, the contact point B of the ball 33 at the outer ball track hasmoved behind the ball center M back to the central joint plane E andalso radially outwards. As a result, the distance N* of the contactpoint B from the central joint plane becomes smaller as compared to theearlier distance N, as shown in FIG. 6. This means that by maintainingthe minimum axial distance L of the contact point from the track andedge, the position of the inner cone 44 can be displaced towards thebase 15, i.e. the outer joint part has been shortened.

FIG. 6 shows the above-mentioned joint articulation angle β between theaxis A_(A) of the outer joint part 31 and the axis A_(I) of the innerjoint part 32. In FIG. 6, the inner joint part is replaced by theconnecting shaft 40 which, in this position, as already mentioned, ispositioned at a distance from the inner cone 44 as a result of thedisplacement of the latter. In consquence, it becomes possible, withoutchanging the articulation angle β, to increase the thickness of theconnecting shaft 40 in order to increase the torque transmittingcapacity. If, in deviating from the illustration, the position of theinner cone is slightly changed while retaining the thickness of theconnecting shaft, and while maintaining an adequate safety distance L ofthe contact point B from the end of the ball track, the articulationangle β can be increased.

Constant Velocity Universal Joint

List of Reference Numbers

11, 31 outer joint part

12, 32 inner joint part

13, 33 ball

14, 34 ball cage

15, 35 base

16, 36 joint journal

17, 37 joint aperture

18, 38 outer ball track

19, 39 inner aperture

20, 40 connecting shaft

21, 41 securing ring

23, 43 cage window

24, 44 inner cone

What is claimed is:
 1. A constant velocity universal joint fortransmitting torque comprising: an outer joint part (31) with outer balltracks (38) the outer joint part having a base end (35) closed by a baseand an open end (37) defined by an aperture; an inner joint part (32)with inner ball tracks (42); torque transmitting balls (33) guided bypairs of outer and inner ball tracks (38, 42) positioned incorresponding meridian planes; and a ball cage (34) which lodges theballs (33) in circumferentially distributed windows (43) and holds theballs in a common plane and guides the balls onto an angle-bisectingplane (W) when the joint is articulated, with the outer and inner balltracks (38, 42) having center lines composed of at least two differentlycurved portions (S_(a), S_(i)) adjoining one another, with the centerlines of the outer and inner ball tracks (38, 42) intersecting oneanother in the center of each ball and being symmetric relative to oneanother with reference to a central joint plane (E), wherein the centerlines (S_(a)) of the ball tracks (38) of the outer joint part (31) eachcomprise convexly curved inner portions (S₁) and, towards the open end(37), oppositely curved concave first end portions (S₂) and that thecenter lines (S_(i)) of the ball tracks (42) of the inner joint part(32) each comprise convexly curved outer portions and, towards the baseend (35) of the outer joint part (31), oppositely curved, concave secondend portions.
 2. A constant velocity universal joint according to claim1, wherein the first end portions (S₂) of the center lines (S_(a)) ofthe ball tracks (38) of the outer joint part (31) continuously adjointhe inner portions (S₁) of the center lines (S_(a)).
 3. A constantvelocity universal joint according to claim 1, wherein the first endportions (S₂) of the center lines (S_(a)) of the ball tracks (38) of theouter joint part (31) adjoin the inner portions (S₁) of the center lines(S_(a)) in a turning point (T).
 4. A constant velocity universal jointaccording to claim 1, wherein tangents on the center lines (S_(a)) areaxis-parallel at respective turning points (T).
 5. A constant velocityuniversal joint according to claim 1, wherein the first end portions(S₂) and inner portions (S₁) of the center lines (S_(a)) of the balltracks (38) of the outer joint part (31) are circular arcs.
 6. Aconstant velocity universal joint according to claim 1, wherein a radiusof curvature (R₂) of the first end portions (S₂) is less than a radiusof curvature (R₁) of the inner portions (S₁) of the center lines (S_(a))of the ball tracks (38) of the outer joint part (31).
 7. A constantvelocity universal joint according to claim 1, wherein the innerportions (S₁) of the ball tracks ( 38) in the outer joint part (31)extend by 10° beyond the central joint plane (E) towards the open end(37) of the outer joint part (31).
 8. A constant velocity universaljoint for transmitting torque comprising: an outer joint part (31) withouter ball tracks (38) the outer joint part having a base end (35)closed by a base and an open end (37) defined by an aperture; an innerjoint part (32) with inner ball tracks (42); torque transmitting balls(33) guided by pairs of outer and inner ball tracks (38, 42) positionedin corresponding meridian planes; and a ball cage (34) which lodges theballs (33) in circumferentially distributed windows (43) and holds theballs in a common plane and guides the balls onto an angle-bisectingplane (W) when the joint is articulated, with the outer and inner balltracks (38, 42) having center lines composed of at least two differentlycurved portions (S_(a), S_(i)) adjoining one another, with the centerlines of the outer and inner ball tracks (38, 42) intersecting oneanother in the center of each ball and being symmetric relative to oneanother with reference to a central joint plane (E), wherein the centerlines (S_(a)) of the ball tracks (38) of the outer joint part (31) eachcomprise curved inner portions (S₁) and, towards the open end (37),oppositely curved first end portions (S₂) and that the center lines(S_(i)) of the ball tracks (42) of the inner joint part (32) eachcomprise curved outer portions and, towards the base end (35) of theouter joint part (31), oppositely curved, second end portions, whereinthe inner portions (S₁) and the outer portions each extend in a curvedway around a center inside the outer joint part (31).
 9. A constantvelocity universal joint according to claim 8, herein the first endportions (S₂) and the second end portions each extend in a cured wayaround a center (Z₂) outside the outer joint part (31).